Effect of low temperatures on the reproduction of summer and perennial rotifers from temperate regions: ecological and life cycle implications

Abstract

Summer and perennial planktonic rotifers from temperate regions can vary greatly in their ability to reproduce at low temperatures. The population growth rate (r day−1) of a Patagonian Keratella tropica was 0.025 at 3.9 °C and gradually increased to 0.083 at 9.3 °C. The ability of this rotifer to survive and reproduce at low winter temperatures suggests that populations in permanent waters with cold winters may have life cycles with little or no commitment to sexually produced diapausing eggs. In contrast, three Brachionus taxa from two localities in southeastern Australia reproduced poorly at low temperatures. At 3.9 °C, all females died before reproducing. At 6.1 °C, only a single amictic female of the Darling Brachionus (B. calyciflorus species complex) from Lake Littra survived to produce a few offspring. At 9.3 °C, amictic females of the Darling Brachionus from both Lake Littra and a billabong produced many more offspring (7–9 offspring female−1) than those of the Lake Littra B. calyciflorus and the billabong B. rubens (1–2 offspring female−1). At 14.9 °C, amictic females of the latter two taxa, and the Darling Brachionus from Lake Littra, produced many (14–17) offspring female−1. Seasonal changes in temperature occurring in natural populations of these Brachionus taxa should have important ecological and evolutionary implications. Low temperatures likely favor the occurrence and reproduction of the Darling taxon. The inability of active individuals to survive and reproduce at low winter temperatures may be a factor favoring selection for sexual reproduction and production of resting eggs in both permanent and temporary water bodies.